The use of external fixation devices in orthopedic procedures for holding bones in position relative to each other has now become common practice. Typically, such devices use a rod positioned parallel to the bones to be fixated and various fixation pins are mounted on the rod with one end of the pin being secured, usually by screw threads, to the bone. The shaft of the fixation pin is then attached on a semi-permanent manner to the rod.
Several problems must be overcome in order to make such a system practical and useful. One of the problems is the weight of the total structure, and another problem is the fact that each fixation pin must be held rigid without slipping or breaking, even under stress, and must be capable of being positioned anywhere along the rod. The fixation pins must be able to be placed at various angles to the bone and must be able to be added or removed independently from all of the other devices connected to the rod. A further problem is that some of the fixation pins are connected to the bone by threads, which, if constructed by the traditional method of cutting the pin shank, would result in a weakened point on the shaft which is susceptible to breaking. Of course, one solution is to make the entire shank heavier. A more practical solution, however, is to use positive threads in which the thread bottoms (valleys) lie along the circumferential periphery of the pin so that the thread tops (ridges) actually have a circumference larger than the circumference of the shank.
Several patents have addressed this issue, particularly U.S. Pat. Nos. 4,745,913, 5,624,440 and 5,047,029. The '913 patent addresses these same issues and discloses a non-round bar for support of the fixation pin. The fact that the bar is not round prevents the pins mounted therealong from entering the fixation surface at selectably different angles. In addition, the mechanism of the '913 disclosure locks the fixation pins to the rod, in part, by a layer of deformable material 15' whose ability to provide continuous, repeatable and dependable grip on the pins is questionable.
The other prior art shows cumbersome arrangements which are both heavy and not very easy to use. Most such prior art arrangements require multiple locking screws for first mounting a clamp and then mounting the fixation pin.
Accordingly, there exists a need in the art for a fixation system that allows for the addition of one or more fixation pins even when other such pins, or other apparatus, is mounted to the rod and fixed to the fixation surface.
There is a further need in the art for such a device that allows for the insertion toward the fixation surface of positive threaded fixation pins without requiring the removal of other such fixation pins already in place.
There is a still further need in the art for a fixation pin holding bolt which can allow a multicircumferential pin to pass therethrough and then tightly grip the pin at three or more distinct points to support the pin without rotation.
A still further need exists in the art for a fixation device which allows for the easy placement of fixation pins therealong in any angle to the fixation surface and lockable with respect to rotational, longitudinal and distance with respect to the fixation surface.